Radioisotopes used in various medical applications are most often produced either with reactors or accelerators, and solid target systems. Most often the targets come in the form of electroplated or melted/sputtered metals deposited on a water-cooled substrate. Alternatively, foils or compacted powders can be irradiated. Examples of such are electroplated Tl-203 to produce Tl-201 and melted Bi-209 to produce At-211.
Moreover, commercial radioisotope production generally involves very labor-intensive processing and therefore is best suited to centralized production of large batch quantities. The radioisotopes produced are subsequently sent to several regional radiopharmacies for further processing and distribution to hospitals and clinics. The relatively long half-life of certain radioisotopes (several hours/days) allows for this distribution system. However, because of their inherent short half-lives (typically less than 2 hrs), the positron emission tomography (PET) isotopes such as F-18, O-15, N-13, and C-11, have to be produced on a local basis close to the hospitals and clinics administering the radiopharmaceuticals.
In order to meet this need, networks of regional production centers have emerged in practically every significant urban area in North America and Europe. These PET centers typically have a small accelerator (cyclotron) and an automated chemistry system required to manufacture a final injectable product. PET targetry only employ fluid (liquid or gas) systems that allow for rapid transfer to the automated chemistry system for processing after the irradiation is complete. Accordingly, these PET cyclotrons systems are generally fitted with commercially-available F-18 production targets and automated chemistry systems to manufacture fluorinated deoxyglucose (FDG).
The F-18 production target is a cylindrical, conical or similar hollow container filled with H218O which is irradiated with a proton beam and forms F-18 by the nuclear reaction 18O(p,n)18F. The irradiated water is transferred to the automated chemistry system, which extracts the 18F and produces the desired end product, 18FDG, in a Good Manufacturing Practices (GMP) environment ready for clinical use. However, viable methods that can take advantage of the foregoing attributes of PET cyclotron FDG systems to prepare other radioisotopes do not currently exist.
Accordingly, new methods of generating useful radioisotopes using a PET cyclotron (or a similar accelerator) and associated targetry and chemistry systems are needed.